This double-blind randomized controlled clinical trial aimed to investigate the effect of whitening dentifrices on the clinical efficiency of in-office tooth bleaching procedures.

Sixty-three eligible participants (29 males and 34 females, mean age 26.1 years) with at least one maxillary tooth demonstrating shade A3 or darker will be recruited and randomly allocated into 3 groups (n = 21), according to the different dentifrices used in this clinical trial: Crest Total (regular dentifrice) for group C, Crest 3D Whitening (conventional whitening dentifrice) for group CW, and Close Up White Now (whitening dentifrice containing blue covarine) for group CU. All participants will receive in-office tooth bleaching with 40% hydrogen peroxide (Opalescence Boost PF 40%) for the maxillary anterior teeth (2 sessions, with a 1-week interval). The participants will be instructed to use only the provided dentifrices and toothbrushes to brush their teeth twice daily over a 4-week period. Colour parameters (CIE L*, a*, b*) will be measured with a spectrophotometer (Vita Easyshade Advance 4.0) at baseline (T1), after the first bleaching session (T2), after the second bleaching session (T3), 1 week after the completion of in-office bleaching (T4), and 3 weeks after the completion of in-office bleaching (T5). The colour differences (ΔE) and whiteness index (W) will also be calculated. The data will be statistically analysed through repeated ANOVA and Tukey's test (α = 0.05).

Inclusion Criteria:

• patients between 18 and 60 years of age, with fully erupted upper and lower incisors and canines without dental or periodontal disease or restorations, and with at least one maxillary tooth presenting color score A3 or darker, as measured with the Vita Classical guide (Vita Zahnfabrik, Bad Sa ̈ ckingen, Germany) ordered by brightness

Exclusion Criteria:

• patients with systemic diseases or oral mucosal disorders, previous bleaching treatment, patients undergoing orthodontic treatment, pregnant women, people with known allergy to the product ingredients, smokers, and alcohol abusers.